Acoustic compensator



April 9, 1940- s. RUTTENBERG 2,196,342

ACOUSTIC COMPENSATOR Filed Jan. 15, 1938 5am zza/fatte@ 567:57

Patented Apr. 9, 1940 UNITED STATES4 PATENT OFFICE" ACOUSTIC OOMPENSATOB samuel Battenberg, New York, N. r. Application January 15. 1938, Serial No. 185,218 5 Clalllll- (Cl. 178-138) This invention relates to a microphone and more particularly to a novel acoustic compensator for the velocity actuated ribbon microphone. and to a pitch or tone control therefor.

5 The velocity actuated ribbon microphone consists in general of a metallic conducting ribbon or thin strip of corrugated metal positioned in a magnetic field and freely accessible to sound waves. When this microphone is placed in a sound field. the dierence in phase between the sound waves impressed on the two sides of the ribbon causes a pressure difference to exist between the two sides and moves the ribbon in the magnetic field. This movement in turn generates an electrical current which may be suitably amplified and reproduced in a manner well known in the art. j

This manner of actuation of the velocity microphone is, of course, dependent on sound waves having free access to both sides of the ribbon, and the ribbon in this type of. microphone is therefore enclosed in a casing which is open both in front and rear and is responsive to sound waves from either front or rear directions.

It has been found that when talking close to a microphone of this type, the low notes or frequencies become objectionably accentuated, giving unsatisfactory reproduction. This is due to `the fact that the low frequency waves cause the ribbon to vibrate as a unit, while at close distances the high frequency waves cause the ribbon to vibrate in sections, and the current generated in one section of the ribbon is opposite in direction to the current generated in the other sections thereof. In other words, when a high frequency wave from a close distance strikes a ribbon, suflicient difference in phase may exist in these small wave length waves to actuate one sec-- tion of the ribbon in a different direction than another section thereof. If the volume is sufiiciently high, therefore, to satisfactorily reproduce high frequencies, it will over-emphasize the low notes. The reproduction of these accentuated low notes or frequencies has a tendency to result in a booming tone, and one of the objects of this invention is, therefore, to overcome this undesirable booming so as to enable these low frequencies and notes to be reproduced naturally and without distortion.

Another object of this invention is to provide an attachment for a velocity actuated ribbon type microphone by means of which such microphone may be converted into a pressure actuated microphone. A further object is to provide a means for gradually decreasing the amplitude of the low frequency response of the velocity microphone so that the change to a pressure operated microphone is effected gradually and at will.

The inventionwill be best understood from the following description in association with the ac- 5 companying drawing, wherein like references refer to like parts, and in which the structure i1- lustrated embodies different forms of the invention.

Figure 1 is a central vertical sectional view, 10 partly diagrammatic, taken through ak velocity or ribbon type microphone, with the tone control mechanism applied thereto;

Figure 2 is an elevation of the rear face of the microphone, showing the means for operating-the l5 tone control; j

Figure 3 is a horizontal sectional view of the microphone taken along the line 3-8 of Figure 2;

Figures 4 and 5 are curves illustrating various characteristics of a microphone according to the go presentv invention;

Figure 6 shows a modified form of the invention.

The invention comprises a microphone casing i of. the type having a ribbon capable of either u velocity or pressure operation, diagrammatically shown at 2. The front and rear faces of the microphone casing have spaced vertically arranged bars I forming a grille. A plate or wall 4 is fixed to the lrear face of the microphone and is 30 spaced from and arranged substantially parallel .to the diaphragm 2. This plate is provided with a large opening 5 which, as presently shown, extends over a third of the area of said wall. The side edges 8, 8 thereof are bent forwardly and 35 towards each other, and are spaced slightly from the main body to provide guiding passageways 1,

1' for a sliding shutter 8 which is supported therein. The shutter carries a U-shaped bracket 8, the base of which is fixed to the shutter, with 40 the arms extending through the casing and loosely embracing one of the vertical bars 3, as shown in Figure 3. The shutter is covered with fabric I8 on both faces. A button lll is secured between the arms of the U-shaped bracket by a 45 rivet Il, or otherwise. Conventional ribbon microphone poles and other conventional mechanism which is located beneath and to each side of the ribbon 2, is indicated at P in Figures 1 and 3. As shown in Figure l, the shutter 8 is in par- 50 tially opened position and the ribbon is therefore partially pressure, and partially velocity, operated. When the shutter is in its uppermost position, the entire back of the microphone is closed and the microphone ribbon is pressure operated Il as the sound waves do not have access to the ribbon from the rear. This pressure operation will tend to minimize the eect of the lower frequencies as compared to the velocity operation (operation with open shutter) and thus eliminate booming.

Figures 4 and 5 mostrate the difference in operation when the shutter is closed or open. As shown, the ribbon has very much greater movement with lower frequencies when operated as a velocity microphone according to Figure 4 and substantial constant movement with both high and low frequencies as shown in Figure 5.

Figure 6 shows a modified form of the invention in which one wall il of the microphone is provided with a series of openings I2, corresponding in function to the grille 3 of Figure l. A rotatable disk i3 is mounted on this wall by a pin il which is used also to rotate the disk, and it is provided with openings which may be aligned with the openings l2 to cause the microphone to be velocity operated, as described above. When the openings i2 are partially closed the microphone is partially pressure and partially velocity operated; when wholly closed, the microphone is pressure operated.

Having thus described my invention, I claim:

1. In a microphone of the vibrating ribbon type capable of velocity or pressure operation, a casing for said ribbon having openings on both sides of the ribbon so as to permit sound waves to have free access to said ribbon, and a shutter movable to close one of said openings to a greater or lesser degree, said shutter when moved to closed position being effective to cause the pressure operation of the ribbon, and when moved to open position to cause the velocity operation thereof.

2. In combination with a microphone of the vibrating ribbon type capable of velocity or pressure operation, a casing therefor having a plurality of openings, one of the openings being on one side of the ribbon and another on the other side thereof so as to permit sound waves to have free access to said ribbon, a closure member for one of said openings comprising a plate having opposed guiding members, said last mentioned opening being intermediate the guiding members and a shutter held in said guiding members and slidable to close said last mentioned opening, said shutter when moved to closed position being effective to cause pressure operation of said ribbon. and when moved to open position to cause velocity operation thereof.

3. In combination with a microphone of the vibrating ribbon type capable of velocity or pressure operation, a casing therefor having a plurality of openings, one of the openings being on one side of the ribbon and another on the other side thereof so as to permit sound waves to have free access to said ribbon. opposed guiding members on each side of one of said openings and a slidable shutter held in said guiding members and slidable to cover said opening, said shutter when moved to closed position being effective to cause the pressure operation of the ribbon, and when moved to open position to cause the velocity operation thereof.

4. In combination with a microphone of the vibrating ribbon type capable of velocity or pressure operation, a casing therefor having a plurality of openings, one of the openings being on one side of the ribbon and another on the other side thereof so as to permit sound waves to have free access to said ribbon, a closure member for one of said openings comprising a plate having opposed side edges thereof bent forwardly and toward each other to form opposed guiding members, said last-mentioned opening being intermediate the guiding members and a shutter held in said guiding members and slidable to close said last mentioned opening, said shutter when moved to closed position being effective to cause the pressure operation of the ribbon, and when moved to open position to cause the velocity operation thereof.

5. In combination with a microphone of the vibrating ribbon type, a casing therefor having openings in two opposite side walls thereof, and a ribbon disposed between said openings, a closure member for one of said openings comprising a rotatable disk with openings spaced to correspond to the openings of one of said walls, whereby upon selective operation of said disk, the microphone may be wholly velocity, wholly pressure, or partly pressure and partly velocity, operated.

SAMUEL RUT'IENBERG. 

